Project Information

Abstract:

Bees pollinate approximately 1/3 of the food we eat. They pollinate all of our fruits, nuts, and vegetables. Honeybees contribute approximately $15 billion in pollination services to U.S. commercial agriculture annually. However, reliance on a single insect species, the honeybee, for the pollination of a huge portion of the human food supply can be dangerous. Indeed, this is especially true considering that honeybees are in decline from Colony Collapse Disorder (CCD), thus putting the global food supply at risk. Today, honeybee colonies are down by 40% compared to the 1970’s.

Over the past four years, the current study has examined the different native bee species in Georgia apple orchards. The mining bees (Family Andrenidae: Genus Andrena) show the greatest promise as a native bee that could replace or supplement the honeybee in early blooming crops (April- May) such as apples, blueberries, etc. Mason bees (Family Megachilidae; Genus Osmia) may also be important in Georgia agriculture when the apple bloom is particularly early (March or April) as seen in 2012 and 2013.

In the 2013 growing season (March-September), 5047 bees from 28 Genera were collected during the survey. The mining bees (58.2% of the sample) clearly dominated the samples taken in the apple orchards. There is little doubt that mining bees are the key native pollinators for early blooming commercial crops in Georgia. Native bee diversity and abundance were similar to previous years, perhaps even a little higher. Mason bee abundance (54 bees collected) was lower than the previous year, but still higher than in 2010 or 2011.

Habitat enrichments were created to boost the abundance of both of these target groups (mining bees and mason bees). Both types of habitat enrichments showed promising results.

Introduction

Honeybees contribute $14.6 billion in pollination services to U.S. commercial agriculture annually [1]. The yields of some crops decrease by more than 90% when honeybees are not present [2]. Reliance on a single insect species, the honeybee, for the pollination of over 1/3 of the human food supply can be dangerous [3]. Indeed, this is especially true considering that honeybees are in decline from Colony Collapse Disorder (CCD), thus putting the global food supply at risk. Today, honeybee colonies are down by 40% compared to colonies available in the 1970’s [4,5]. In 2007, CCD resulted in sharp declines in honeybees in at least 35 states, including Georgia. In the affected areas, 50% of beekeepers reported significant colony losses [6].

The reduced availability of honeybee colonies has increased food production costs and reduced potential crop yields. Most farmers are dependent on rented honeybee hives in order to ensure their crops are fully pollinated. The shortage of honeybee colonies has resulted in a rapid increase in the cost of renting honeybee hives. For example, the cost of renting a single honey bee colony used in almond pollination in California increased from $35 in the early 1990’s to $150 per colony in 2007 [6]. The potential loss or reduction of the honeybee can have a devastating effect on agricultural production. We need to develop alternative strategies that are less dependent on the use of the honeybee in order to ensure long-term sustainably of insect pollinated crops.

The best alternative to honeybees is the native bees already present in the local environment [7-11]. With nearly 3500 species in North America alone, the diversity of different forms, pollen-strategies, and behaviors of native bees provide a wide range of use for agricultural operations. It is estimated that native bees already annually contribute $3 billion to U.S. agriculture [12].

In addition, native bees may exhibit much greater pollination efficiency compared to honeybees [13]. For example in apple pollination, one female Osmia cornifrons is estimated to pollinate 2450 apple per day, compared to 80 apples per day by a honeybee [14].

Every region, even every crop, has its own characteristic group of native bee pollinators.

Data concerning regional make-ups of these native pollinator-guilds are severely lacking, which has led to our reliance on the European honeybee. In fact, across the continent, available information on native bees is spotty at best [15]. Therefore, research is needed to determine which native bees are present in a given region and how best to enrich the habitat (e.g. nesting areas) to increase target native bee populations.

Our studies have identified the mining bee, Andrena crataegi, and its close relatives, the Melandrena, as being the ideal native bee(s) for North Georgia apple production. Other excellent apple pollinating native bees identified were the carpenter bees, bumblebees, and mason bees. It is time to expand the study to the next step: to develop habitat enrichments and other strategies to increase the abundance of targeted native bees in commercial apple orchards.

By establishing a strong network of native bees in Georgia agriculture, we can make Georgia Agriculture more secure and sustainable. In addition, an increase in reliance on native bees means that farmers will spend less money on pollination services (e.g. renting honey bee hives) that will increase farmer profits and potentially reduce food costs for the general public.

Literature Cited

1. Morse R.A. and N.W. Calderone. The Value of Honey Bees as Pollinators of U.S. Crops in 2000. Bee Culture 128:1-15.

7. Kremen, C., N.M. Williams, and R.W. Thorp. 2002. Crop Pollination from Native Bees at Risk from Agricultural Intensification. Proceedings of the National Academy of Sciences of the United States of America 99 (26): 16812-16816.

15. National Academy of Science. 2007. Status of pollinators in North America. National Academies Press, Washington, DC.

Project Objectives:

Main objective

The main objective of the study is to create habitat/nesting enrichments that will maximize the overall abundance of the previously identified target bee species (mining bees and mason bees). These nesting/habitat enrichment areas are hypothesized to increase the abundance of the targeted native bees already present in the orchard.

In order to boost the abundance of the main native bee target species, the mining bees (Andrena crataegi and other mining bee species), soil enrichments sites will be needed. These bees prefer patches of soil in which to dig tunnels for their habitat and a place to brood their young. At each orchard, four trenches (about 12 inches deep and 60inches long X 18 inches wide) will be excavated.

In order to boost the abundance of the secondary target bee species (mason bees), four special nesting boxes for the bees will be created within each plot. The center of the nesting box will contain a large section of about sixty tubes (varying from 6mm to 8 mm) or wooden boxes with 40-80 holes (8 mm diameter).

Secondary objective

The secondary objective is to continue the survey of the native bee pollinators for a fourth year within the apple orchards, with a focus placed specifically on the apple bloom periods.

Cooperators

Click linked name(s) to expand

Nick Stewart

Taxonomist

Georgia Gwinnett College

Research

Materials and methods:

The proposed study has targeted one main goal and one secondary goal.

The main goal of the study is to implement protocols to maximize the overall abundance of the previously identified target bee species through the use of habitat/nesting enrichments.

The secondary goal is to continue the survey of the native bee pollinators for a fourth year within the apple orchards, with a focus placed specifically on the apple bloom periods. Significant weather changes, perhaps due to global warming, have resulted in drastically different growing seasons. The apple bloom has shifted 4-5 weeks earlier in the past two years from the typical bloom in April. These much earlier apple blooms can impact which native bees are present to pollinated them (e.g. The mason bees, Osmia species, are more important during early apple blooms).

MAIN GOAL – Measuring the Success of Native Bees in Apple Pollination

To achieve the first goal, experiments will be performed at four North Georgia Apple Orchards.

In these orchards, outside the typical collection plot (now – our control plots), we will set up habitat enrichment areas tailored specially to the target Apple-pollinating bees. In the new area at each apple orchard, four four-foot long soil enrichment areas (see below for details) and four specifically designed wooden nest boxes (see below for details) will be created for each orchard. These nesting/habitat enrichment areas are hypothesized to increase the abundance of the targeted native bees already present in the orchard.

In order to boost the abundance of the main native bee target species, the mining bees (Andrena Crataegi and other Melandrena species), soil enrichments sites will be needed. These bees prefer patches of soil in which to dig tunnels for their habitat and a place to brood their young. At each orchard, four trenches (about 12 inches deep and ten feet long) will be excavated. Mixed with the 12 inches of native soil extracted from the trench, 6 inches of sand will be added in order to create an18 inch tall hill next to the trench. Based on previous studies, this raised, bare-soil and trench combination should attract the mining bees.

In order to boost the abundance of the secondary target bee species (mason and carpenter bees) four special nesting boxes for the bees will be created within each plot. The center of the nesting box will contain a large section of about sixty 9-inch tubes constructed of industrial “Kraft-paper” with glassine-paper inserts (to facilitate brood development checks, population counts, and easy removal of the next generation of Osmia). These inserts are shown to be the preferred nesting designs for the mason bees (Osmia species). The actual supports of the nesting box, made from 4X4 posts of untreated pine-wood, will contain enough optimal nesting substrates to serve as a main nesting area for the carpenter bees.

In order to assess the success of the collection tubes in the nest box for boosting the abundance of the mason bees (Osmia species), we will examine each individual tube to get an exact count of the Osmia. This type of examination does not hurt or injure the bees. Most of these bees will be returned back to their originating orchard. Some larvae will be raised to adulthood in order to identify their species.

In order to assess the success of the untreated wooden frame for boosting the abundance of the carpenter bees (Xylocopa virginica), we will examine the wooden nest box for new holes, as well as the pre-drilled hole sites. We will excavate some of the contents of the holes to measure larvae abundance.

In order to assess the success of the soil enrichment area for boosting the abundance of the mining bees (Andrena crategii and the Melandrena), we will examine the soil for holes (entrances to the colony). We will excavate some areas of the soil to measure larvae abundance.

SECONDARY GOAL – Survey of Native Bees in Georgia Apple Orchards

To achieve the secondary goal, a survey of native bees will be conducted in four North Georgia Apple Orchards.

In these orchards, native bees will be collected using several types of insect collecting traps and procedures, including pan-traps, vane-traps, malaise-traps, and timed sweep-netting. Insect diversity and abundance will be measured 2 weeks prior to and after the bloom, and weekly during the bloom itself. The traps will be set up around dawn and will remain up until after dusk during collection days, which is a typical 12-hour collection period.

At each orchard, there will be a total of 13 sets of pan-traps (six elevated 3-feet and seven placed at ground level). Each set includes 1 white, yellow, and blue pan painted with UV-reactive paint. In each orchard, 6 sets of vane traps will be used. Each set includes 1 blue vane trap and 1 yellow vane trap. Likewise, 2 malaise traps will be set-up (1 trap in the center of the orchard with the other trap near the edge of the plot) for each sample day.

After the collection, all the bees, including those collected in the vane traps, will be brought back to the GGC laboratory to be counted and identified. Bees will be determined to species and either preserved in ethanol or pinned and mounted in permanent collection boxes. Species will be compared to reference collections. Difficult to identify species will be sent to Sam Droege at the USGS Bee Monitoring and Inventory Laboratory (Beltsville, MD) for identification.

Research results and discussion:

Main objective

Mining bee (Andrena species) Enrichments

Four trenches were created at each orchard, in order to boost the abundance of the mining bees (Andrena crataegi) and other mining bee species. Mining bees prefer patches of soil in which to dig tunnels for their habitat and a place to brood their young. Two trenches were placed at opposite sides of the sampling plot in each orchard. On one side, floral enrichments (e.g. 2 cherry trees and 2 bushes that bloom before apple trees) were added around the trenches, while on the other side, the “control group side”, no trees or bushes were added around the trenches. At each orchard, significant nesting took place in the trenches. Both mining bees and sweat bees were observed to nest in the trenches. In addition, nesting frequency was more than double on average in “floral enrichment” trenches compared to the control group trenches without floral resources. Bee nesting increased in the trenches throughout the apple bloom. Nesting in the trenches ended mid-May.

Mason bees (Osmia species) Enrichments

Eight nest boxes were created at each orchard in order to boost the abundance of the secondary target bee species (mason bees). Four nesting boxes were placed at opposite sides of the sampling plot in each orchard. Three of the nest boxes contained a wooden block with 8mm holes drilled into the length of the box, and one nest box contained 60 nesting tubes (6 mm, 7mm, and 8mm tubes). On one side, floral enrichments (e.g. 2 cherry trees and 2 bushes that bloom before apple trees) were added around the nest boxes, while on the other side, the “control group side”, no trees or bushes were added around the nest boxes. At each orchard significant nesting took place in the nest boxes.

Five mason bee species nested in the nesting boxes. The two most common species nesting in the nest boxes were Osmia georgica and O. taurus. Significant parasitism took place in all orchards. Parasitism was much greater in wooden nesting boxes compared to the nesting tubes. 136 Osmia cocoons successfully developed. The highest level of nesting took place in 6 mm tubes, predominately by Osmia georgica. The second highest level of nesting took place in 8 mm tubes or wooden nest boxes, predominately by Osmia taurus.

Secondary objective

During the 2013 growing season (March-September), 4169 bees from 28 Genera were collected during the survey. The 3 most common groups were Genus Andrena (mining bees) (46.4% of the sample), Genus Lasioglossum (sweat bees) (19.7% of the sample), and Genus Apis (honey bees) (12.0% of the sample). Andrena crataegi continued to be the most common bee species collected in the apple orchard. See Table 1 for more information.

Four orchards were sampled approximately 9 times (4 times during the bloom) from March to September 2013. Mountain View Orchard (small-scale “typical” Georgia orchard) exhibited very high levels of native bees (both diversity and abundance); while Mercier Orchard (largest orchard in Georgia) exhibited very low native bee abundance. Mercier Orchards had similar bee diversity levels (at least at the genus level) as Mountain View Orchards. However, Mercier had only 10% of the abundance that Mountain View exhibited. This may suggest that large-scale orchards require habitat enrichments in order to maintain target native bee groups in useful numbers.

Stewart, N.G. and M.A. Schlueter. Diversity and abundance of native bees in orchards are significantly impacted by the timing of the apple bloom. 61th Annual Meeting of the Entomological Society of America, Austin, TX. Nov. 9-14, 2013.

Stewart, N.G. and M.A. Schlueter. Fluctuations in Species Abundances of Major Apple Pollinating Native Bees During Progessively Earlier Apple Blooms Over a Three Year Period in North Georgia. 2013 Annual Meeting – Association of Southeastern Biologist. Charleston, WV. April 10-13, 2013.

Stewart, N.G. and M.A. Schlueter. Identification of a Native Bee Species to Serve as the Primary Pollinator for Commercial Apple Cultivation in North Georgia. 2013 Annual Meeting – Association of Southeastern Biologist. Charleston, WV. April 10-13, 2013.

Project Outcomes

Project outcomes:

This project has taken the first step in the identification of native bees that have the potential to replace or supplement honeybees in apple pollination in Georgia. Next, researchers need to develop procedures and methods to increase the abundance of these target native bees. The current project has shown that by providing habitat enrichments (e.g. nesting sites), we can boost native bee abundance. Once researchers have developed a methodology to identify and maximize the abundance of target native bees for a broad range of Georgia crops, we can state sustainable agriculture in Georgia is safeguarded.

By establishing a strong network of native bees in Georgia agriculture, we can make Georgia Agriculture more secure and sustainable. In addition, an increase in reliance on native bees means that farmers will spend less money on pollination services (e.g. renting honey bee hives) that will increase farmer profits and potentially reduce food costs for the general public.

Economic Analysis

In the Unites States alone, honeybees contribute nearly $15 billion in pollination services. The yields of some crops decrease by more than 90% when honeybees are not present. The reliance on a single insect species, the honeybee, for the pollination of over 1/3 of the human food supply can be dangerous. In the United States, there has been a sharp decline in managed honeybee colonies, from 4 million honeybee colonies in the 1970’s to 2.4 million colonies in 2005.

The reduced availability of honeybee colonies has increased food production costs and reduced potential crop yields. Most farmers are dependent on rented honeybee hives in order to ensure their crops are fully pollinated. The shortage of honeybee colonies has resulted in a rapid increase in the cost of renting honeybee hives. For example, the cost of renting a single honey bee colony used in almond pollination in California increased from $35 in the early 1990’s to $150 per colony in 2007 [4,5].

If native bees can be harnessed as the primary pollinator, or even as a supplement pollinator of targeted food crops, farmers will reduce their production costs by reducing or eliminating the use of rented hives. Consider the annual savings if native bees can pollinate roughly half of a farmer’s crops. For example, a farmer who requires 100 rented hives for crop pollination might pay (100 hives @ $150 = $15,000) before adding habitat enrichments (e.g. nesting areas) for native bees. If the native bees provide half the pollination required, the farmer spends only $7,500 (50 hives at $150) each year on pollination services.

Farmer Adoption

Based on this study, farmers at our experimental orchards have observed the significant role that native bees play in the pollination of their orchards. The long-term goal of our research in shifting pollination services to native bees from honeybees is appealing to farmers because of the significant cost savings and better long-term sustainability. In order to boost the abundance of “target” native bee populations, certain habitat modifications will be necessary. The most important of these modifications is providing more nesting habitat for native bees. During the next several growing season, the farmers have agreed to allow the placement of several different experimental nesting habitats. Also, the farmer cooperators will make a special effort to implement procedures to enhance native bee abundance (particularly just before, during, and just after the apple bloom). These changes will include: reducing grass mowing of the orchard (allows wildflowers to supplement native bee food sources) and reducing pesticide use.

Recommendations:

Areas needing additional study

Results from this project and from other studies have documented that native bees have the potential to supplement and/or replace the honeybee in commercial agriculture. This study has clearly identified which species of native bees are most suited for the pollination of commercial apple orchards in Georgia. These target bees include: Andrena crataegi, mining bees (Andrena species), bumblebees (Bombus species), and carpenter bees (Xylocopa species). Mason bees (Osmia species) may also have potential. The next step is to develop appropriate habitat modifications (supplemental nesting sites, additional pre-bloom floral resources) in order to boost the abundance of these target native bee species. If methods can be developed to boost the abundance of these target native bee species, farmers can begin to shift their pollination services from the struggling honeybee to native bees. These changes will safeguard Georgia’s agriculture and will provide a more cost-efficient sustainable method of pollinating Georgia’s apple crops.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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